1. Field of the Invention
The present invention relates to a network device in a data network and more particularly to a system and method of logically linking multiple ports into a signal port of the network device and transmitting multicast packets through the logical port.
2. Description of the Related Art
A packet switched network may include one or more network devices, such as a Ethernet switching chip, each of which includes several modules that are used to process information that is transmitted through the device. Specifically, the device includes an ingress module, a Memory Management Unit (MMU) and an egress module. The ingress module includes switching functionality for determining to which destination port a packet should be directed. The MMU is used for storing packet information and performing resource checks. The egress module is used for performing packet modification and for transmitting the packet to at least one appropriate destination port. One of the ports on the device may be a CPU port that enables the device to send and receive information to and from external switching/routing control entities or CPUs.
A current network device may support physical ports and logical/trunk ports, wherein the trunk ports are a set of physical external ports that act as a single link layer port. Ingress and destination ports on the network device may be physical external ports or trunk ports. By logically combining multiple physical ports into a trunk port, the network may provide greater bandwidth for connecting multiple devices. Furthermore, if one port in the trunk fails, information may still be sent between connected devices through other active ports of the trunk. As such, trunk ports also enable the network to provide greater redundancy between connected network devices.
In order to transmit information from one network device to another, the sending device has to determine if the packet is being transmitted to a trunk destination port. If the destination port is a trunk port, the sending network device must dynamically select a physical external port in the trunk on which to transmit the packet. The dynamic selection must account for load sharing between ports in a trunk so that outgoing packets are distributed across the trunk.
Typically, each packet entering a network device may be one of a unicast packet, a broadcast packet, a muliticast packet, or an unknown unicast packet. The unicast packet is one that is to be transmitted to a specific destination address that can be determined by an ingress network device. The broadcast packet is typically sent to all ports by the ingress network device and the multicast packet is sent to multiple identifiable ports by the ingress network device. To multicast or broadcast a packets specific bits in the packet are set prior to transmission of the packet to the ingress network device. An unknown unicast packet is a unicast packet in which the ingress network device cannot determine the port associated with the destination address. So the ingress network device broadcasts the packet which is ignored by all ports except the intended but previously unknown destination port. When the previously unknown destination port sends a response message to the ingress network device, all network devices “learn” the associated destination address. Thereafter, any unicast packet sent to the previously unknown port is transmitted as a traditional unicast packet.
When a broadcast/multicast packet is to be sent on a trunk group that includes multiple physical ports, the ingress device must send the packet to every device in the network with sending duplicate copies of the packet on a given trunk. Current network devices include two types of multicast methods: a layer 2 multicast/broadcast/unknown unicast and a layer 3 multicast. As such, network devices include three masks: one for layer 3, layer 2 and broadcast. The network devices use these masks to select a destination port on which to send the packet. However, these masks are limiting and do not provide for adequate distribution of the traffic on a given trunk group